The present invention relates to power tools such as impact wrenches, and more particularly to plastic housings for power tools.
Pneumatic tools, such as impact wrenches, are well known in the prior art. An impact wrench, for example, includes an air driven motor having an air inlet port and an air exhaust that vents to the atmosphere. High pressure air drives the motor as the air moves from a high pressure inlet, through the motor and is exhausted to atmosphere. An impact clutch assembly is coupled to an output shaft of the air motor. These tools are commonly used in an industrial setting, where a source of pressurized air may be used to power a number of individual units. Impact wrenches are particularly useful, because a number of different bits, sockets or attachments may be used to perform a variety of tasks.
Impact wrenches conventionally comprise a housing having a handle, an air motor housed in an upper portion of the housing, and an impact clutch assembly mounted to the front of the housing and operatively connected to the air motor. Impact wrench housings have traditionally been cast metal, such as aluminum. It is necessary that the housing be rigid to support the air motor and impact clutch, and withstand significant vibrations and other forces generated in the operation of the tool. It is also necessary that the housing accurately define the centerline of the air motor and impact clutch assembly. The air motor includes a longitudinal rotor shaft that meshes with and drives the impact clutch assembly. For proper operation of the tool, the air motor shaft must be accurately aligned with the impact clutch.
It would be desirable to reduce the weight and manufacturing costs of impact wrenches by molding the housing from plastic materials. However, prior efforts with plastic housings have met with limited success. One problem is that it is difficult to tightly control tolerances with molded plastic parts. Plastic parts can become distorted in the molding process, particularly after the part is removed from the mold and cooled. Second, plastic housings even when accurately molded, can become distorted during use, particularly when subjected to heat and severe vibratory and mechanical forces experienced during normal operation of impact wrenches or other pneumatically powered tools.
If the housing becomes distorted either in molding or in operation of the tool, it can cause misalignment between the air motor shaft and impact clutch assembly. If the motor and clutch are out of alignment excessive loads will be placed on the motor and/or clutch assemblies, resulting in undesirable wear, and in extreme cases, fatigue and failure. Furthermore, misalignment of the motor shaft often causes air leakage, which reduces the power and efficiency of the tool.
It would therefore be desirable to have a light weight plastic housing that will maintain accurate alignment of a motor and clutch assembly in a power tool.
These and other objects are met or exceeded by the present invention, which features a rigid preformed insert for a molded plastic housing for a power tool. The power tool comprises a housing molded substantially of plastic, a preformed insert molded into the housing, and a motor having a shaft, the motor being at least partly supported by the insert. The motor is preferably an air motor. The power tool further comprises an impact clutch attached to the housing and operatively coupled to the motor shaft. The motor and clutch have a common axis, with the preformed insert located between the motor and the clutch. The insert fixedly secures the axis of the output shaft of the motor. The insert also forms a seal between the motor and clutch.
The housing is molded plastic, preferably a fiberglass and nylon composite. The insert may be preformed to close tolerances from a dimensionally stable material. Most preferably, the insert is machined aluminum. The housing is manufactured by first forming and machining the insert, positioning the insert in a housing mold to define the motor axis, injecting the housing mold with plastic to form the housing and permanently secure the insert therein, and installing the output end of the motor into the back of the insert. An impact clutch assembly is then fastened to the housing, installed in the front of the insert, and operatively coupled to the motor shaft.
The insert of the invention solves the problems experienced with prior art plastic housings. Because the insert is preformed, for example by machining the insert from metal, the insert will not warp, distort or otherwise lose tolerance as a result of the molding process for the plastic housing. Further, because the insert is preformed of rigid, dimensionally stable material, is precisely orientated within the housing mold, and is permanently molded into the housing, it accurately defines the motor-clutch axis minimizing if not preventing misalignment of the motor shaft. Excessive wear and air leakage are avoided.
The objects of the invention have accordingly been met in a facile manner. Other attributes and benefits of the present invention will become apparent from the following detailed specification when read in conjunction with the accompanying drawings.